Journal of Crop Breeding

Rice bacterial blight caused by Xanthamonos oryzae pv. oryzae is one of the most destructive bacterial diseases of rice in some areas of rice cultivation in the world, especially in the tropics of Asia. The low efficiency of disease management methods, especially chemical methods, has led to more research on recognizing resistant cultivars and understanding resistance mechanisms through the study of biochemical interactions and recognition of resistant genes. This study aimed to evaluate the resistance of 24 commercial Iranian rice cultivars against bacterial blight and to study some mechanisms of resistance at biochemical levels and the pattern of PAL gene expression by the qRT-PCR method. The results of the greenhouse assessment showed that different cultivars varied in the development of leaf spot length as the most important trait for disease evaluation. The Khazar and Nemat commercial cultivars at the highest level of resistance and the Tarom (mahalli) and Dilamani cultivars showed the highest sensitivity based on the evaluation index (quantitative resistance) of this disease. Biochemical evaluation of Catalase, guaiacol peroxidase, superoxide dismutase enzymes and total phenol in the resistant and sensitive cultivar shows the high activity of these enzymes in the resistant cultivar compared to the sensitive cultivar in the early hours after inoculation. The difference between resistant and sensitive cultivars was significant at the level of one percent. The PAL gene expression rate was also significantly higher in the resistant Caspian cultivar in the early hours (12h) after inoculation than the sensitive cultivar. Overall, it seems that the induction of the PAL gene and the subsequent increase in the accumulation of oxidative and antioxidant enzymes in the resistance of Khazar cultivar to the sensitive cultivar of Tarom, it is part of the defense mechanism of rice against Xoo bacteria.